In DC/DC converters, a DC input voltage is converted to a lower DC output voltage. Normally, the output voltage needs to be precisely regulated and input to output isolation is necessary in order to meet safety requirements.
FIG. 1 is a schematic diagram of a prior art two stage converter 100. The two stage converter 100 comprises a power factor correction (PFC) boost converter 120 and an isolated buck-type converter 140. The PFC boost converter 120 provides a high voltage DC current to the isolated buck-type converter 140. The isolated buck-type converter 140 converts the high voltage DC current into a low-voltage DC current.
In this and other prior art converters, the switches of the second stage work under hard switching conditions, resulting in high switching losses, and thereby affecting the total efficiency of the converter and limiting the switching frequency. Additionally, the second stage needs a current-limiting circuit to provide over-current protection during abnormal conditions, such as during an output short circuit. This need for over-current protection increases the complexity of the control circuit.
What is needed in the art is a simplified DC/DC converter design that reduces switching losses.